I really meant just the air fare if one has to cancel because of sickness, etc, without insurance. Is the cost lost in full?

It depends on the ticket class and the airline. For example, with a non-refundable fare Delta will issue a credit (minus a cancellation fee) that must be used within one year of issue date. I think the cancellation fee is $100 but don't quote me on that. So you don't lose the total value but Delta still has total control of your money.